2D Titanium carbide printed flexible ultrawideband monopole antenna for wireless communications

Flexible titanium carbide (Ti3C2) antenna offers a breakthrough in the penetration of information communications for the spread of Internet of Things (IoT) applications. Current configurations are constrained to multi-layer complicated designs due to the limited conformal integration of the dielectric substrate and additive-free Ti3C2 inks. Here, we report the flexible ultrawideband Ti3C2 monopole antenna by combining strategies of interfacial modification and advanced extrusion printing technology. The polydopamine, as molecular glue nano-binder, contributes the tight adhesion interactions between Ti3C2 film and commercial circuit boards for high spatial uniformity and mechanical flexibility. The bandwidth and center frequency of Ti3C2 antenna can be well maintained and the gain differences fluctuate within ±0.2 dBi at the low frequency range after the bent antenna returns to the flat state, which conquers the traditional inelastic Cu antenna. It also achieves the demo instance for the fluent and stable real-time wireless transmission in bending states.


Reviewer #1 (Remarks to the Author): A 2D Titanium Carbide Printed Flexible
Ultrawideband monopole antenna for wireless communication is proposed. It is highly appreciated that much effort has been put and it is evident in the measurements performed. Following comments for the authors to take into consideration before a revision is submitted.

Response:
We would first like to thank the reviewer for the positive comment on the significance and quality of our work. Your insightful comments are very constructive for the further improvement of our work. We have tried our best to revise our manuscript accordingly.

Why circular patch of given size is chosen. It is suggested to provide the evolution of the design with respect to the reflection coefficient performance and material properties
in comparison with the impedance matching may also be discussed.

Answer:
We would like to thank the reviewer for this insightful suggestion. The given size of the circular patch is shown in Supplementary Fig. 11 in the revised Supporting Information. The design principles are as follows.
In 1992, Honda first proposed an ultrawideband circular monopole antenna with an extraordinary impedance bandwidth and omnidirectional radiation performance due to the symmetrical current distribution on the disk (Proc. Int. Symp. Antennas Propag., 4, 1145(1992). In comparison with the circular patch, the elliptical patch has similar symmetrical currents and improved impedance bandwidth due to the better impedance matching performance (IEEE Trans. Antennas Propag. 46, 294-295 (1998)) (See the notes in Supplementary Fig. 12 in the revised Supporting Information).

Supplementary Fig. 12 | The design principles of the ultrawideband elliptical Ti3C2
monopole antennas. a, Simulated S11 of the Ti3C2 antennas with different axial ratios and measured S11 of the Ti3C2 antennas with axial ratio of 1.3. b, Comparison of the measured and simulated S11 of the Ti3C2 antennas by the parameters of conductivity and sheet resistance. 3 For the design of an ultrawideband monopole antenna, the specific size of the antenna is determined by the following equations (2) and (3).
Where k is taken as 0.823 empirically for a dielectric layer with εr = 2.2 and h = 0.254 mm. L is the long axis of the ellipse, b = L/2, and r is the effective radius of an equivalent cylindrical monopole antenna. p is the length of the 50 Ω feed line. We first assume that L = 3.9 cm, p = 0.1 cm, and r ≈ 0.375 cm can be determined by equation (2). Then, the value of a ≈ 1.5 cm can be determined by equation (3)  In order to obtain the widest impedance bandwidth, the axial ratio of the elliptical Ti3C2 antennas is first analyzed and the simulated reflection coefficient S11 is shown in Supplementary Fig. 12a in the revised Supporting Information. When the axial ratio of the ellipse is less than 1.3, the relative bandwidth of the antennas widens with the increase of axial ratio. S11 of the antennas is greater than -10 dB in 3-4 GHz. However, when the axial ratio of the ellipse is greater than 1.3, the relative bandwidth of the antennas is almost unchanged. Considering the miniaturization requirement of the antennas, the axial ratio of the ellipse is set as 1.3. (See the notes in Supplementary Fig.   12 in the revised Supporting Information) The material system and full-wave simulation are combined based on sheet resistance for the first time to accurately predict the performance of Ti3C2-10 μm antennas ( Supplementary Fig. 12b). In comparison with conductivity, the sheet resistance is more accurate for full-wave simulation in Ti3C2 microwave performance analysis. The actual bandwidth of Ti3C2-10 μm antennas is consistent with the simulated bandwidth. Thus, the design rationality of antenna size is verified (See the notes in Supplementary Fig. 12 in the revised Supporting Information).
In comparison with the poor flexibility and sophisticated manufacturing process of metal, the flexibility, scalability, and ease of solution processing of Ti3C2 nanosheets 4 are promising for lightweight and flexible antenna components to support the rapid development of integrated RF devices. Ti3C2 antennas have the potentials to be an alternative to conventional metal antennas for efficient and reliable power delivery at higher frequencies in RF and 5G communication. Fig.4.f and also mention the plane (E-plane and H-plane) for the figures.

Provide the units in
Answer: We appreciate the reviewer's wise comment. The unit is dBi. The left pattern in Fig. 4f is E-plane and the right pattern in Fig. 4f is H-plane as shown in Fig. 4f in the revised manuscript.  Answer: We sincerely appreciate the reviewer for the insightful suggestion. ( )

3) Have you made a comparison between simulations and characterization regarding directivity and axial ratio of the antenna?
Answer: We are very grateful for the reviewer's wise suggestion.
The comparison between simulations and characterization regarding directivity of the Ti3C2 antenna has been made. The directivity of an antenna is equal to the ratio of the maximum power density to its average value over a sphere as observed in the far field of an antenna (Kraus, J. D. & Marhefka, R. J. Antennas: For All Applications, Third Edition). The gain of an antenna is an actual or realized quantity which is less than the directivity due to ohmic losses in the antenna. The relationship between directivity and gain can be derived according to the equation (S1), where D is the directivity of the antenna, G is the gain of the antenna, k is the radiation efficiency of the antenna. The measured and simulated directivity of Ti3C2 antennas is shown in Supplementary Fig. 16  The comparison between simulations and characterization of axial ratio has also been made. The axial ratio of the antenna is defined as the ratio of the length of the major axis and minor axis of the ellipse. In order to obtain the widest impedance bandwidth, the axial ratio of the elliptical Ti3C2 antennas is first analyzed and the simulated reflection coefficient S11 is shown in Supplementary Fig. 12a in the revised Supporting Information. When the axial ratio of the ellipse is less than 1.3, the relative bandwidth of the antennas widens with the increase of axial ratio. S11 of the antennas is greater than -10 dB in 3-4 GHz. However, when the axial ratio of the ellipse is greater than 1.3, the relative bandwidth of the antennas is almost unchanged. Considering the miniaturization requirement of the antennas, the axial ratio of the ellipse is set as 1.3.
(See the notes in Supplementary Fig. 12 in the revised Supporting Information) The Therefore, the antenna proposed in this work is a linearly polarized antenna.  (2022) antennas by the parameters of conductivity and sheet resistance. Fig.4 why does using a lower thickness of MXene membrane cause a deeper notch between 2 to 2.5 GHz?

In
Answer: We are very grateful for the reviewer's professional comment. The bandwidth of the ultrawideband monopole antenna results from the superposition of multiple resonance points, which will cause S11 curve to rise upward. As the Ti3C2 layer becomes thinner, the local resonance characteristics become stronger. As shown in Fig where Qt is the total Q value, Qr is the radiation loss, Qd is the dielectric loss, Qc is the conductor loss, and Qs is the surface-wave loss. For the design of an ultrawideband monopole antenna, the specific size of the antenna is determined by the following equations (2) and (3).
Where k is taken as 0.823 empirically for a dielectric layer with εr = 2.2 and h = 0.254 mm. L is the long axis of the ellipse, b = L/2, and r is the effective radius of an equivalent cylindrical monopole antenna. p is the length of the 50 Ω feed line. We first assume that L = 3.9 cm, p = 0.1 cm, and r ≈ 0.375 cm can be determined by equation (2). Then, the value of a ≈ 1.5 cm can be determined by equation (3)  In order to obtain the widest impedance bandwidth, the axial ratio of the elliptical Ti3C2 antennas is first analyzed and the simulated reflection coefficient S11 is shown in Supplementary Fig. 12a in the revised Supporting Information. When the axial ratio of the ellipse is less than 1.3, the relative bandwidth of the antennas widens with the increase of axial ratio. S11 of the antennas is greater than -10 dB in 3-4 GHz. However, when the axial ratio of the ellipse is greater than 1.3, the relative bandwidth of the antennas is almost unchanged. Considering the miniaturization requirement of the antennas, the axial ratio of the ellipse is set as 1.3. (See the notes in Supplementary Fig.   12 in the revised Supporting Information) The material system and full-wave simulation are combined based on sheet resistance for the first time to accurately predict the performance of Ti3C2-10 μm antennas ( Supplementary Fig. 12b). In comparison with conductivity, the sheet resistance is more accurate for full-wave simulation in Ti3C2 microwave performance analysis. The actual bandwidth of Ti3C2-10 μm antennas is consistent with the simulated bandwidth. Thus, the design rationality of antenna size is verified (See the notes in Supplementary Fig. 12 in the revised Supporting Information). The according changes have been made in our revised manuscript: "which may be further increased through improving the conductivity of Ti3C2 layer or adopting suitable substrates with lower dielectric loss." (Page 11, line 16~18) 5. In "Adv. Mater., vol. 33, no. 1, pp. 1-7, 2021, doi: 10.1002." the authors purposed antennas with higher radiation efficiency a. What would be the advantage of your work to theirs?

The authors presented antennas with a gain below 4 dB and radiation
Answer: We sincerely appreciate the reviewer for the wise suggestion. The work (Adv. Mater., 33, 1, 1-7 (2022)) does show a unique advantage of higher radiation efficiency.
However, its bandwidth is very narrow and can only radiate in the upper half of the substrate. In order to satisfy different frequency requirements, the microstrip antennas of different sizes need to be designed. Moreover, the construction of flexible Ti3C2 antenna involves in the utilization of polyethylene terephthalate and double-sided tape between Ti3C2 layer and commercial circuit boards, which causes the complicated manufacture process as well as hinders the direct conformal integration with flexible 25 electronics and chips. In comparison, the ultrawideband Ti3C2 monopole antenna in our work has many specific advantages as follows.
First, the most intuitive advantage is that it can cover many commercial frequency bands at the same time, such as WiFi, Bluetooth, WCDMA, 4G TD-LTE, 5G (n41, n78).
According to Shannon's equation,

Does humidity or heat affect the antenna's performance over time?
Answer: We sincerely appreciate the reviewer for the insightful suggestion. The humidity and heat effect on the antenna performance over time has been validated in an isolated custom-made chamber.
The humidity effect on the antenna performance has been evaluated through the implementation of Ti3C2 antenna as radiating and sensing element while the antenna sensor is connected to the vector network analyzer (Supplementary Fig. S30a). The antenna sensor is positioned inside the sealed custom-made chamber, and the humidity is pumped by the humidifier. Resonant peak is used as the initial frequency to measure the resonant frequency shift during humidity sensing measurement ( Supplementary Fig.   S30b,c). When the humidity is less than 60%, the bandwidth of the antenna remains unchanged, and the amplitude of the resonance point of S11 increases sharply. When the humidity is greater than 60%, the bandwidth of the antenna becomes smaller and the S11 curve changes slowly. As the humidity further increases to 90%, the amplitude of the S11 curve of the antenna correspondingly increases, and the resonance point takes a The heat effect on the antenna performance has been measured through the implementation of Ti3C2 antenna as radiating and sensing element while the antenna sensor is connected to the vector network analyzer ( Supplementary Fig. S31a). The antenna is irradiated by an infrared lamp (317 mW cm -2 ) as a heat source, and the thermal imager is used to monitor the real-time temperature (Supplementary Fig. S31b).
As the temperature of the antenna rises, the amplitude of S11 curve decreases and the resonance point takes a right-shift ( Supplementary Fig. S31c,d). The humidity effect on the antenna performance has been evaluated through the implementation of Ti3C2 antenna as radiating and sensing element while the antenna sensor is connected to the vector network analyzer (Supplementary Fig. S30a). The antenna sensor is positioned inside the sealed custom-made chamber, and the humidity is pumped by the humidifier. Resonant peak is used as the initial frequency to measure the resonant frequency shift during humidity sensing measurement ( Supplementary Fig.   S30b,c). When the humidity is less than 60%, the bandwidth of the antenna remains unchanged, and the amplitude of the resonance point of S11 increases sharply. When the humidity is greater than 60%, the bandwidth of the antenna becomes smaller and the S11 curve changes slowly. As the humidity further increases to 90%, the amplitude of the S11 curve of the antenna correspondingly increases, and the resonance The heat effect on the antenna performance has been measured through the implementation of Ti3C2 antennas as radiating and sensing elements while the antenna sensor is connected to the vector network analyzer (Supplementary Fig. S31a). The antenna is irradiated by an infrared lamp (317 mW cm -2 ) as a heat source, and the thermal imager is used to monitor the real-time temperature (Supplementary Fig. S31b).
As the temperature of the antenna rises, the amplitude of S11 curve decreases and the resonance point takes a right-shift ( Supplementary Fig. S31c,d). Answer: We sincerely appreciate the reviewer for the insightful suggestion. is less than 4 m, the transmission effect of the antenna is very fluent, the points on the planisphere are very concentrated, the error rate is almost 0, and the video transmission is very stable (Supplementary Fig. 28a-d). When the distance is extended to 5 m, the video transmission becomes slightly unstable, but the overall transmission effect is still acceptable (Supplementary Fig. 28e). (See the notes in Supplementary Fig. 28  Lpath (dB) = 32.45 + 20lgr (km) + 20lgf (MHz) (S2) 33 where r represents the distance between the two antennas, and f represents the operating frequency of two antennas.
where Pr represents the receiving power, Pt represents the transmitting power, 10lgGr represents the gain of the receiving antenna, 10lgGt represents the gain of the transmitting antenna.  Fig. 14). The long-range stability will continue to be tested in our future work.

Supplementary Fig. 14 |
The reflection coefficient S11 repeatable for one month.  The skin depth is calculated by the Equation (S4), where σ, µ, and f are conductivity, permeability, and frequency, respectively (Sci. Adv.  In this work, the gain error margin for the ultrawideband Ti3C2 monopole antenna is rational and acceptable. We will further reduce the gain difference through process optimization in our future work.

4, eaau0920 (2018)). (See the notes in Supplementary
Finally, we would like to thank the reviewer again for these valuable comments